1. Field of the Invention
The present invention relates to a digital broadcast receiving apparatus for receiving stream data of a plurality of channels in a digital broadcast system such as digital satellite broadcast system or cable television system.
2. Description of the Related Art
When handling video data and audio data in digital satellite broadcast system cable TV system and the like, compression coding is widely used to compress the amount of information by reducing information redundancy of an enormous amount of data. As this compression coding method, for example, MPEG2 (Moving Picture Experts Group-2) standards defined in ISO/IEC 13818 and so on have been well known.
In the MPEG2 standards, not only the compression coding method of video data and audio data, but also the multiplexing method of coded data is standardized in xe2x80x9cISO/IEC 13818-1: 1994 Information technology Coding of moving pictures and associated audio Part 1: Systemsxe2x80x9d (MPEG2 system).
By using this multiplexing technique, video data and audio data compressed in amount of information by using the compression coding method are subjected to time division multiplexing. As a result, it is possible to Multiplex a plurality of sets (programs) of video data and audio data associated therewith in one carrier (one channel) and transmit the multiplexed data (program multiplexing).
In such an MPEG2 system, a program stream (PS) system and a transport stream (TS) system are defined as a technique for packet multiplexing.
In each of these systems, video data or audio data subjected to compression coding are packetized into PS (Program Stream) packets or TS (Transport Stream) packets, and these packets are then multiplexed. Typically, in a broadcasting system, a TS system capable of multi-program has been used.
There has been disclosed a device for receiving video data, audio data, and added value service data from a bit stream formed of a plurality of programs in Japanese Patent Application Unexamined Publication No. 8-275147. More specifically, this conventional receiving device is provided with data selection means for selecting a coded stream, multiplexed data, and added value information corresponding to one channel from a multiplexed data stream, and demultiplexes desired TS packets to extract video data, audio data, and added data.
Packet-multiplexed data are inputted in a bit stream form, from a transmission medium of digital satellite broadcasting or cable TV system. This bit stream has been obtained by adding error correction codes to TS packets of the MPEG2 standards and applying transmission path modulation to resultant TS packets. The inputted bit stream is demodulated and subjected to error correction processing, and supplied as TS system data to a packet demultiplexer. In order to obtain desired video and/or audio data from program-multiplexed TS packets, the packet demultiplexer separates and extracts desired TS packets and sends them to a subsequent stage.
The format of a TS packet will be described briefly by referring to FIGS. 9A, 9B and 9C, before describing a conventional digital broadcast receiver.
In FIG. 9A, each TS packet has a fixed length of 188 bytes. TS packets and 16-byte error correction codes are arranged alternately. Each TS packet is basically formed of a 4-byte transport stream header (TS header) and a payload including data to be transmitted. As necessary, an extension header called adaptation field is inserted between the TS header and the payload. Within the TS header, a packet ID (PID) which is an identifier indicating the attribute of the TS packet is represented by 13 bits. Data included In the payload is classified into two types as shown in FIG. 9B and FIG. 9C, according to information to be transmitted.
FIG. 9B shows the case where a part of a PES (Packetized Elementary Stream) packet is included in a payload. This PES packet includes a PES header and coded video data or coded audio data, which is an element of contents of a program to be transmitted. The PES header includes the kind of an element included within the PES packet and a PES packet length. This PES packet is divided into payloads of TS packets provided with different PIDs according to kinds of elements included within the PES packet. Resultant payloads are carried by TS packets.
FIG. 9C shows the case where a payload includes program specific information (PSI) which is specific information for system control and service information (SI) which is information specific to service such as program information. Hereafter, the information PSI and the information SI are referred to collectively as xe2x80x9cPSI/SI data.xe2x80x9d
The PSI/SI data is tabulated every unit called xe2x80x9csection.xe2x80x9d In the same way as the case of PES, the PSI/SI data is divided into payloads of TS packets respectively provided with different PIDs, according to included information contents and resultant payloads are stored in TS packets. Besides the PSI/SI data which is the contents of the section, each section includes a section header at its head. In the section header, a table ID representing the table kind of the section and a section length indicating the section length are described At the end of the section, cyclic redundancy check (CRC) bits are included.
The PSI data has the structure of a hierarchical table. For each program (set of video and audio data), the PSI data includes a program map table (PMT) describing correspondence between elements with PIDs (packet IDs) and a program association table (PAT) describing corresponding between the PMTs with PIDS.
Further, in the case where transmitted TS packets are encrypted (scrambled), key information for solving the encrypted data is needed. In such a case, however, the PSI includes an entitlement control message (ECM) representing descramble information of each program and an entitlement management message (EMM) representing key information of each contracting subscriber.
Further, in the case where a plurality of scramble systems, relations between ECMs and EMMs corresponding to these scramble systems are described by using a conditional access table (CAT).
In this way, each TS packet has a payload including an element as shown in FIG. 9B or a payload including information (system control data) for system control as shown in FIG. 9C. These can be distinguished by the PID. In a TS packet having system control data, the contents of each section can be distinguished by the section header.
FIG. 1 shows an example of a conventional digital broadcast receiving apparatus comprised of a demodulator 101, a packet demultiplexer 102, a CPU 103, a ROM 140, and a RAM 105. In the packet demultiplexer 102, the PID of a TS packet storing a desired program is stored in a PID table 112. Upon receiving program-multiplexed TS packets from the demodulator 101, a PID filter 111 compares the PID of a TS packet received from the demodulator 101 with the PIDs stored in the PID table 112 and extracts a TS packet matching one of the PIDs of the PID table 112. A plurality of necessary PIDs are previously written by the CPU 103 into the PID table 112 via a data bus and a bus I/F 114.
The ROM 104 stores a system control program for controlling the operations of the digital broadcast receiving apparatus by running on the CPU 103. The CPU 103 operates in accordance with the system control program.
Among TS packets extracted by the PID filter 111, TS packets including elementary data such as video data or audio data are successively supplied to a decoder I/F 113, subjected to removal (demultiplexing) of TS header and adaptation field, and are then sent to the outside through an elementary output port.
ATS packet Including PSI/SI data in Its payload, which has been extracted by the PID filter 111, is once stored in a packet storage area of the RAM 105 via the bus I/F 114 and subjected to section reconfiguration in the CPU 103. Out of the reconfigured section, only information required for system control is processed by the CPU 103, and the reconfigured section is stored back into a different storage .area of the RAM 105 and is then analyzed by the CPU 103 and thereby information required for system control is extracted.
Further, as the configuration of a multiplexed-packet demultiplexer, there is known a configuration having descrambling means for the case where data obtained by conducting scramble processing on information to be transmitted is received.
FIG. 2 shows another example of the conventional apparatus. In FIG. 2, reference numeral 106 denotes a descrambler. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and the descriptions of the same components will be omitted.
In the case where scramble processing has been conducted on information to be transmitted, a received TS packet subjected to processing of demodulation and error correction in the demodulator 101 has been scrambled.
The CPU 103 can know information corresponding to the scramble system by receiving a CAT In the transmitted TS system in the same way as that shown in FIG. 1.
On the basis of the CAT, ECM, and EMM, the CPU 103 analyzes the Information key required for descrambling to obtain a scramble releasing key, and sets the PID of a program corresponding to the scramble releasing key in the descrambler 106 via the bus. Even if information to be transmitted has been subjected to scramble processing, therefore, it is possible to receive data while releasing the scramble.
However, the above-described conventional apparatus has such a configuration as to take in received stream data as it is. For inputting packet data included in stream data of a plurality of channels which can have IDs having the same value, therefore, the conventional apparatus needs to have as many combinations of encryption release means, data packet extraction means, ID storage means operating on the basis of ID of each data packet as the number of input channels. As a result, the conventional apparatus has a problem that its circuit becomes large in scale.
The present invention has been made in view of the above-described problems.
An object of the present Invention is to provide a digital broadcast receiving apparatus capable of simultaneously inputting packet data included in stream data of a plurality of channels which can have the same ID.
According to the present invention, a digital broadcast receiver for inputting stream data of a plurality of channels from a plurality of demodulators, includes: a converter for converting packet identification information of stream data inputted from a demodulator; a multiplexer for multiplexing stream data converted by the converter and stream data inputted from another demodulator to a single stream of data; a stream divider for dividing the single stream of data into necessary packets, first packets having packet identification information converted by the converter, and second packets inputted from the other demodulator; a reverse converter for converting the converted packet identification information of a first packet to original packet identification information; and a transfer means for transferring packets outputted by the reverse converter and second packets outputted by the stream divider to separately storing them in a memory.
According to an aspect of the present invention, a digital broadcast receiver includes: a demodulator for demodulating a modulated signal to produce first stream data including a plurality of packets on each of the channels, wherein each of the packets is one of an element signal packet and a control signal packet; a conversion table for storing conversion information for predetermined packet identification information; a converter for converting packet identification information of a packet in first stream data on a predetermined channel to temporary identification information to produce second stream data when the packet identification information of the packet matches the predetermined packet identification information stored in the conversion table; a multiplexer for multiplexing the first stream data and the second stream data to third stream data; a packet distributor for distributing each of control signal packets included in the third stream data depending on which of the first and second stream data the packet is included in: a reverse converter for converting the temporary identification information of a control signal packet distributed by the packet distributor and included in the second stream data to original packet identification information; and a memory for separately storing control signal packets included in the first stream data and control signal packets which has been converted by the reverse converter.
The conversion table may include a first table containing the predetermined packet identification information identifying a plurality of packets on a plurality of channels; and a second table containing the temporary identification information with which the predetermined packet identification information is replaced, the temporary identification information uniquely identifying a single packet.
The conversion table may include: a filter table containing predetermined filter packet identification information identifying an element signal packet: a first table containing the predetermined packet identification information identifying a plurality of packets on a plurality of channels; and a second table containing the temporary identification information with which the predetermined packet identification information is replaced, the temporary identification information uniquely identifying a single packet.
The multiplexer multiplexes the first stream data and tho second stream data to the third stream data and produces a data select signal indicating which of the first and second stream data is selected in the third stream data. The packet distributor distributes each of packets included in the third stream data to a decoder depending on whether the packet is the element signal packet, by referring to the filter table of the conversion table and then distributes each of remaining packets in the third stream data to a first output and a second output, depending on the data select signal received from the multiplexer.
According to another aspect of the present invention, a digital broadcast receiver Includes: a demodulator for demodulating a modulated signal to produce first stream data including a plurality of packets on each of the channels, wherein each of the packets is one of an element signal packet and a control signal packet; a conversion table for storing conversion information for predetermined packet identification information; a converter for converting packet identification information of a packet in first stream data on a predetermined channel to temporary identification information to produce second stream data when the packet identification information of the packet matches the predetermined packet identification information stored in the conversion table; a multiplexer for multiplexing the first stream data and the second stream data to third stream data; a descrambler for descrambling the third stream data according to a preset descrambling key; a packet distributor for distributing each of control signal packets included in the descrambled third stream data depending on which of the first and second stream data the packet is included in; a reverse converter for converting the temporary identification information of a control signal packet distributed by the packet distributor and included in the second stream data to original packet identification information; and a memory for separately storing control signal packets included in the first stream data and control signal packets which has been converted by the reverse converter.
According to the present invention, packets having the same packet ID on different channels are each provided with unique packet IDs over the different channels. Therefore, a plurality of channels can be handled as a single stream of data multiplexed by the multiplexer, resulting in reduced circuit amount and lower cost.